Third generation partnership project (3GPP) mobile communication systems based on a wideband code division multiple access (WCDMA) radio access technology are widely spread all over the world. High-speed downlink packet access (HSDPA) that can be defined as a first evolutionary stage of WCDMA provides 3GPP with a radio access technique that is highly competitive in the mid-term future. However, since requirements and expectations of users and service providers are continuously increased and developments of competing radio access techniques are continuously in progress, new technical evolutions in 3GPP are required to secure competitiveness in the future.
In general, there are one or more cells within the coverage of a base station (BS). A plurality of user equipments (UEs) may be located in one cell. A UE accesses to a network by performing a random access process. The random access process may be used when the UE adjusts time synchronization with the network or when the UE obtains radio resources if there is no radio resource for uplink communication.
When the UE is powered on for initial access to a new cell, the UE is downlink synchronized and receives system information of the cell to be accessed. According to the received system information, the UE requests to the BS an uplink radio resource for transmitting a radio resource control (RRC) connection request message through a random access channel (RACH). The BS receives the request for the uplink radio resource and allocates a suitable radio resource to the UE so that the UE can transmit the RRC connection request message. Then, the UE transmits the RRC connection request message to the BS by using the radio resource. The BS transmits a message indicating that the random access of the UE is successful. Upon successfully performing the random access, the UE can transmit a control message to a network. However, in order for the UE to transmit and receive actual user data, an RRC connection has to be completely established between the UE and the network. The RRC connection between the UE and the network is completely established by configuring a non-access stratum (NAS) layer which is an upper layer of an RRC layer. For this, the UE transmits a NAS service request message to the BS, and the BS transmits it to the network. The NAS service request message is a message for requesting configuration of the NAS layer so that user data can be transmitted between the UE and the network.
In general, a delay time required to perform an RRC connection establishment process for switching from an idle state to an active state is 100 ms or less. In the RRC connection establishment process, the delay time between the network and the BS may significantly vary with the development of functions of the network. The delay time is expected to be not short. However, at present, there is no clearly proposed mechanism for satisfying the delay time required in the RRC connection establishment process.
A time for performing the RRC connection establishment process between the UE and the network is equal to a delay time directly experienced by a user. The delay time needs to be minimized to improve system quality. Accordingly, there is a need for a method for improving system quality with a minimum delay time.